Defines Multisite subdomain constants and handles warnings and notices.

VHOST is deprecated in favor of SUBDOMAIN_INSTALL, which is a bool.

On first call, the constants are checked and defined. On second call,
we will have translations loaded and can trigger warnings easily.

function ms_subdomain_constants() {
	static $subdomain_error      = null;
	static $subdomain_error_warn = null;

	if ( false === $subdomain_error ) {
		return;
	}

	if ( $subdomain_error ) {
		$vhost_deprecated = sprintf(
			/* translators: 1: VHOST, 2: SUBDOMAIN_INSTALL, 3: wp-config.php, 4: is_subdomain_install() */
			__( 'The constant %1$s is deprecated. Use the boolean constant %2$s in %3$s to enable a subdomain configuration. Use %4$s to check whether a subdomain configuration is enabled.' ),
			'VHOST',
			'SUBDOMAIN_INSTALL',
			'wp-config.php',
			'is_subdomain_install()'
		);

		if ( $subdomain_error_warn ) {
			trigger_error(
				sprintf(
					/* translators: 1: VHOST, 2: SUBDOMAIN_INSTALL */
					__( 'Conflicting values for the constants %1$s and %2$s. The value of %2$s will be assumed to be your subdomain configuration setting.' ),
					'VHOST',
					'SUBDOMAIN_INSTALL'
				) . ' ' . $vhost_deprecated,
				E_USER_WARNING
			);
		} else {
			_deprecated_argument( 'define()', '3.0.0', $vhost_deprecated );
		}

		return;
	}

	if ( defined( 'SUBDOMAIN_INSTALL' ) && defined( 'VHOST' ) ) {
		$subdomain_error = true;
		if ( SUBDOMAIN_INSTALL !== ( 'yes' === VHOST ) ) {
			$subdomain_error_warn = true;
		}
	} elseif ( defined( 'SUBDOMAIN_INSTALL' ) ) {
		$subdomain_error = false;
		define( 'VHOST', SUBDOMAIN_INSTALL ? 'yes' : 'no' );
	} elseif ( defined( 'VHOST' ) ) {
		$subdomain_error = true;
		define( 'SUBDOMAIN_INSTALL', 'yes' === VHOST );
	} else {
		$subdomain_error = false;
		define( 'SUBDOMAIN_INSTALL', false );
		define( 'VHOST', 'no' );
	}
}